Regulator of a sense amplifier

ABSTRACT

A system and method for operating a memory cell is provided. A non-volatile memory storage device includes an array of memory cells of differential or single-ended type. In an embodiment, a regulator is coupled to a sense amplifier. The regulator is configured to generate a voltage to gate terminals of one or two transistors of the sense amplifier. In the differential type, the voltage is generated such that the first bias current and the second bias current have a current value equal to the sum of a maximum current flowing in a memory cell being in a RESET state and a fixed current. In the single-ended type, the regulated voltage is generated such that the first bias current and the second bias current have a current value equal to the sum of a fixed current and the reference current generated by the reference current source across temperature.

TECHNICAL FIELD

The present disclosure generally relates to non-volatile memory and, in particular embodiments, to a regulator of a sense amplifier used in non-volatile memory.

BACKGROUND

A variety of non-volatile memories are available today, such as phase-change memories (PCMs), where the characteristics of materials having the property of switching between phases with a different electrical behavior are exploited for storing information. These materials can switch between a disorderly or amorphous phase and an orderly crystalline or polycrystalline phase.

Different phases are characterized by different resistivity values and are associated with different stored datum values. The elements of Groups XV and XVI of the periodic table, such as tellurium (Te), selenium (Se), and antimony (Sb), also known as pnictogens and chalcogens, can be used for manufacturing phase-change memory cells. In particular, an alloy formed by germanium (Ge), antimony (Sb), and tellurium (Te), known as GST (having the chemical composition Ge2Sb2Te₅), is currently widely used in such memory cells.

The phase changes can be obtained by locally increasing the temperature of the cells of chalcogen materials through resistive electrodes (i.e., heaters) set in contact with corresponding regions of the chalcogen material.

Access or selection devices (for example, bipolar or metal oxide semiconductor transistors) are connected to the resistive electrodes and selectively enable the passage of a programming electric current (i.e., write electric current) through them. By the Joule effect, the electric current generates the temperature required for phase change to switch from a high-resistivity state (i.e., RESET state) to a low-resistivity state (i.e., SET state) or vice versa.

During a read operation, the state of the chalcogen material is detected by applying a low voltage and then reading the value of the current that flows in the memory cell through a sense amplifier. Given that the current is proportional to the conductivity of the chalcogen material, it is possible to determine the state of the material and consequently the datum stored in the memory cell.

SUMMARY

A first aspect relates to a non-volatile memory storage device, which includes an array of memory cells of a differential type, a sense amplifier, and a regulator. The array of memory cells includes a plurality of pair of memory cells, and each pair of memory cells includes a first memory cell and a second memory cell. The first memory cell is in one of a SET state or a RESET state and the second memory cell is in a state other than that of the first memory cell. The sense amplifier includes a first branch coupled to a first memory cell and a second branch coupled to a second memory cell. The sense amplifier is configured to generate a first bias current in the first branch by a first transistor of the sense amplifier, generate a second bias current in the second branch by a second transistor of the sense amplifier-the first bias current being the same as the second bias current. The sense amplifier is further configured to sense a first delta current corresponding to a difference between the first bias current and a current flowing in the first memory cell, and sense a second delta current corresponding to a difference between the second bias current and a current flowing in the second memory cell. The regulator is coupled to the sense amplifier and is configured to generate a regulated voltage to gate terminals of the first transistor and the second transistor of the sense amplifier. The regulated voltage generated is such that the first bias current and the second bias current have a current value equal to the sum of a maximum current flowing in a memory cell being in a RESET state and a fixed current.

In a first implementation form of the non-volatile memory storage according to the first aspect as such, a value of the fixed current is between 5 and 80 microamps.

In a second implementation form of the non-volatile memory storage device according to the first aspect as such or any preceding implementation form of the first aspect, the source terminals of the first transistor and the second transistor are coupled to a supply voltage having a voltage of approximately 1 Volts.

In a third implementation form of the non-volatile memory storage device according to the first aspect as such or any preceding implementation form of the first aspect, the regulator includes an operational amplifier (op-amp) having a non-inverting input coupled to a drain terminal of the first transistor and an inverting input coupled to a reference voltage.

In a fourth implementation form of the non-volatile memory storage device according to the first aspect as such or any preceding implementation form of the first aspect, the first memory cell is in a SET state and the second memory cell is in the RESET state, and the current flowing in the first memory cell is greater than the current flowing in the second memory cell.

In a fifth implementation form of the non-volatile memory storage device according to the first aspect as such or any preceding implementation form of the first aspect, the first memory cell is in a SET state and the second memory cell is in the RESET state, and the second memory cell is a lesser conductive memory cell than the first memory cell.

In a sixth implementation form of the non-volatile memory storage device according to the first aspect as such or any preceding implementation form of the first aspect, the non-volatile memory storage device further includes a memory used to store a list of reference voltage values corresponding to each particular pair of memory cells of the array of memory cells, and the regulated voltage is generated such that the current value being equal to the sum of the maximum current flowing in the memory cell being in the RESET state is particular to each memory cell pairing of the array of memory cells.

A second aspect relates to a non-volatile memory storage device, which includes an array of memory cells of a single-ended type, a sense amplifier, and a regulator. Each memory cell is in one of a SET state or a RESET state. The sense amplifier includes a first branch coupled to a memory cell and a second branch coupled to a reference current source. The sense amplifier is configured to generate a first bias current in the first branch by a first transistor of the sense amplifier, generate a second bias current in the second branch by a second transistor of the sense amplifier-the first bias current is the same as the second bias current. The sense amplifier is further configured to sense a first delta current corresponding to a difference between the first bias current and a current flowing in the memory cell, and sense a second delta current corresponding to a difference between the second bias current and a reference current generated by the reference current source. The regulator is coupled to the sense amplifier and is configured to generate a regulated voltage to gate terminals of the first transistor and the second transistor of the sense amplifier. The regulated voltage is generated such that the first bias current and the second bias current have a current value equal to the sum of a fixed current and the reference current generated by the reference current source across temperature.

In a first implementation form of the non-volatile memory storage according to the second aspect as such, a value of the fixed current is between 5 and 80 microamps.

In a second implementation form of the non-volatile memory storage device according to the second aspect as such or any preceding implementation form of the second aspect, the source terminals of the first transistor and the second transistor are coupled to a supply voltage having a voltage of approximately 1 Volts.

In a third implementation form of the non-volatile memory storage device according to the second aspect as such or any preceding implementation form of the second aspect, the regulator includes an operational amplifier (op-amp) having a non-inverting input and an inverting input. The non-inverting input is coupled to a drain terminal of the first transistor and the reference current source, and the inverting input is coupled to a reference voltage.

In a fourth implementation form of the non-volatile memory storage device according to the second aspect as such or any preceding implementation form of the second aspect, the reference current generated by the reference current is adjusted based on a temperature reading of the non-volatile memory storage device.

In a fifth implementation form of the non-volatile memory storage device according to the second aspect as such or any preceding implementation form of the second aspect, the regulator includes an operational amplifier (op-amp) having a non-inverting input coupled to a drain terminal of the first transistor. The non-inverting input is coupled in a shunt configuration with the reference current source.

In a sixth implementation form of the non-volatile memory storage device according to the second aspect as such or any preceding implementation form of the second aspect, the reference current source includes a multiplexer and a configurable current sink. The multiplexer is configured to adjust the configurable current sink based on a sensed temperature of the non-volatile memory storage device.

A third aspect relates to a device, which includes an array of memory cells of a single-ended type, a sense amplifier, a regulator, and a controller. Each memory cell is in one of a SET state or a RESET state. The sense amplifier includes a first branch coupled to a memory cell and a second branch coupled to a reference current source. The sense amplifier is configured to generate a first bias current in the first branch by a first transistor of the sense amplifier, generate a second bias current in the second branch by a second transistor of the sense amplifier-the first bias current being the same as the second bias current. The sense amplifier is further configured to sense first delta current corresponding to a difference between the first bias current and a current flowing in the memory cell, and sense a second delta current corresponding to a difference between the second bias current and a reference current generated by the reference current source. The regulator is coupled to the sense amplifier and is configured to generate a regulated voltage to gate terminals of the first transistor and the second transistor of the sense amplifier. The regulated voltage is generated such that the first bias current and the second bias current have a current value equal to the sum of a fixed current and the reference current generated by the reference current across temperatures. The controller is coupled to the regulator, sense amplifier, and the array of memory cells. The controller is configured to generate a control signal to the regulator to generate the regulated voltage.

In a first implementation form of the device according to the third aspect as such, a value of the fixed current is between 5 and 80 microamps.

In a second implementation form of the device according to the third aspect as such or any preceding implementation form of the third aspect, the source terminals of the first transistor and the second transistor are coupled to a supply voltage having a voltage of approximately 1 Volts.

In a third implementation form of the device according to the third aspect as such or any preceding implementation form of the third aspect, the regulator includes an operational amplifier (op-amp) having a non-inverting input coupled to a drain terminal of the first transistor. The non-inverting input further coupled in a shunt configuration with the reference current source.

In a fourth implementation form of the device according to the third aspect as such or any preceding implementation form of the third aspect, the reference current source includes a multiplexer and a configurable current sink. The multiplexer is configured to adjust the configurable current sink based on a sensed temperature of the array of memory cells.

In a fifth implementation form of the device according to the third aspect as such or any preceding implementation form of the third aspect, the reference current generated by the reference current source is adjusted based on a temperature reading of the array of memory cells.

Embodiments can be implemented in hardware, software, or in any combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a non-volatile memory storage device;

FIG. 2 is a column decoder, as may be arranged in the non-volatile memory storage of FIG. 1 ;

FIG. 3 is an embodiment sense amplifier for reading differential-type memory cells;

FIG. 4 is an embodiment intermediate circuit of the sense amplifier of FIG. 3 ;

FIG. 5 is an embodiment timing diagram for signals used during a read operation;

FIG. 6 is an embodiment latch circuit of a sense amplifier;

FIG. 7 is an embodiment regulator, as may be implemented in the sense amplifier of FIG. 3 ;

FIG. 8 is an embodiment sense amplifier for reading single-ended type memory cells;

FIG. 9 is an embodiment regulator, as may be implemented in combination with a plurality of sense amplifiers, among which an example is presented in FIG. 8 ;

FIG. 10 is an embodiment current sink circuit, as may be implemented in the sense amplifier of FIG. 8 ;

FIG. 11 is an embodiment current sink circuit, as may be implemented in the regulator of FIG. 9 ; and

FIG. 12 is an electronic device 1100 incorporating the non-volatile memory storage device of FIG. 1 .

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

This disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The particular embodiments are merely illustrative of specific configurations and do not limit the scope of the claimed embodiments. Features from different embodiments may be combined to form further embodiments unless noted otherwise.

Variations or modifications described to one of the embodiments may also apply to other embodiments. Further, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of this disclosure as defined by the appended claims.

While inventive aspects are described primarily in the context of a phase-change memory type, the inventive aspects may be similarly applicable to other types of memory such as FLASH, PCM with a bipolar junction transistor (BJT), magnetoresistive RAM (MRAM), resistive random access memory (RRAM), or the like.

Embodiments provide a sense amplifier and a method for operating for accessing a memory device. In an embodiment, a non-volatile memory storage device includes an array of memory cells of a differential type. In such an embodiment, the array of memory cells includes a plurality of pair of memory cells, one or more sense amplifiers, and a regulator.

Each pair of memory cells includes a first memory cell and a second memory cell. The first memory cell is in one of a SET state or a RESET state and the second memory cell is in a state other than that of the first memory cell. The array of memory cells includes one or more sense amplifiers.

Each sense amplifier includes a first branch coupled to a first memory cell and a second branch coupled to a second memory cell. The sense amplifier is configured to generate a first bias current in the first branch by a first transistor of the sense amplifier, generate a second bias current in the second branch by a second transistor of the sense amplifier, where the first bias current is the same as the second bias current. The sense amplifier is further configured to sense a first delta current corresponding to a difference between the first bias current and a current flowing in the first memory cell, and sense a second delta current corresponding to a difference between the second bias current and a current flowing in the second memory cell.

The regulator is coupled to the sense amplifier and is configured to generate a regulated voltage to gate terminals of the first transistor and the second transistor of the sense amplifier. The regulated voltage is generated such that the first bias current and the second bias current have a current value equal to the sum of a maximum current flowing in a memory cell being in a RESET state and a fixed current.

In another embodiment, a non-volatile memory storage device includes an array of memory cells of a single-ended type. In such an embodiment, the array of memory cells includes a plurality of pair of memory cells, one or more sense amplifiers, and a regulator. Each memory cell is in one of a SET state or a RESET state.

Each sense amplifier includes a first branch coupled to a memory cell and a second branch coupled to a reference current source. The sense amplifier is configured to generate a first bias current in the first branch by a first transistor of the sense amplifier, generate a second bias current in the second branch by a second transistor of the sense amplifier, where the first bias current is the same as the second bias current. The sense amplifier is further configured to sense a first delta current corresponding to a difference between the first bias current and a current flowing in the memory cell, and sense a second delta current corresponding to a difference between the second bias current and a reference current generated by the reference current source.

The regulator is coupled to the sense amplifier and is configured to generate a regulated voltage to gate terminals of the first transistor and the second transistor of the sense amplifier. The regulated voltage is generated such that the first bias current and the second bias current have a current value equal to the sum of a fixed current and the reference current generated by the reference current source across temperature. These and other details are discussed in greater detail below.

FIG. 1 illustrates a non-volatile memory storage device 100. The non-volatile memory storage device 100 includes a memory array 102 formed by memory cells 104. The memory cells 104 are arranged in rows (i.e., wordlines (WL)) and columns (i.e., bit lines (BL)/local bit lines (LBL). Each memory cell 104 includes a storage element 108 a and an access element 108 b. The storage element 108 a and the access element 108 b are arranged in series between a respective local bit line (LBL) and a ground terminal. A wordline (WL) is defined by the set of all control terminals of the access elements 108 b that are aligned within the same (i.e., identical) row.

The access element 108 b is an N-channel metal oxide semiconductor (MOS) transistor. The gate terminal, drain terminal, and source terminal of the access element 108 b are, respectively, coupled to a respective wordline (WL), the first terminal of the storage element 108 a, and the ground terminal. The second terminal of the storage element 108 a is coupled to a respective local bit line (LBL). The access element 108 b is controlled and biased to enable when selected, the passage of a read current or a write current through the storage element 108 a.

The non-volatile memory storage device 100 includes a control logic 106, a column decoder 112, and a row decoder 110. The column decoder 112 and the row decoder 110 enable the selection of the memory cells 104 based on address signals (AS) received from the control logic 106. The control logic 106 may include a finite state machine (FSM) circuit 120 to control various operations disclosed herein. The control logic 106 may additionally include an on-board memory 122 to store instructions or configurations for the operation of the control logic 106.

In particular, the control logic 106 enables reading and writing of the memory cells 104 through the address signals (AS). The row decoder 110 and the column decoder 112 enable bias of a memory cell of the memory cells 104 at appropriate voltage values based on a selected wordline (WL) and local bit line (LBL) designated by the address signals (AS). Further, the control logic 106 communicates control signals to the row decoder 110 and the column decoder 112 to control the read and write operations of the memory cells 104.

The column decoder 112 operates in a read mode and a write mode. In the read mode, a read path provides a conductive path between a selected local bit line (LBL) and the read stage circuit 114.

In the write mode, a write path provides a conductive path between a selected local bit line (LBL) and the write stage circuit 116. The write stage circuit 116 is configured to supply currents required for write operations (i.e., programming of the memory cells 104 in corresponding logic stages) and storage of information.

Thus, the column decoder 112 includes selection elements (e.g., controlled transistors) for the read and write paths, which are connected to implement an address-decoding system—typically hierarchical—for the selection of the memory cells 104.

Typically, the memory array 102 is organized in a plurality of sectors, each of which includes multiple memory cells 104. Each sector is associated with a corresponding portion of the row decoder 110 where the respective wordlines (WL) arrive. Moreover, each sector includes a plurality of respective wordlines (WL) and respective local bit lines (LBL)-distinct from those of other sectors, which are physically connected to the memory cell 104 of the sector. For each set of a number K of local bit lines (LBL), two main bit lines (MBL) are provided: one for reading and one for writing. However, the read and write do not require different main bit lines (MBL).

The local bit lines (LBL) of each sector are specific for that sector (i.e., not shared between different sectors). Instead, the main bit lines (MBL) can be shared between two or more sectors (i.e., electrically coupled to local bit lines (LBL) of both of the sectors, provided that this does not coincide).

FIG. 2 illustrates a column decoder 112, as may be arranged in the non-volatile memory storage device 100. As shown, each local bit line (LBL) of memory cell 104 is connected to a respective main read bit line (MBL_(r)) and a respective main write bit line (MBL_(w)) via, respectively, a switch 204 b and a switch 204 a. The switch 204 a is a metal oxide semiconductor transistor of the P-type, and the switch 204 b is a metal oxide semiconductor transistor of the N-type.

The switch 204 a and the switch 204 b implement the first level of a hierarchical decoding system implemented by the column decoder 112. The column decoder 112 includes a read decoding circuit 206 and a write decoding circuit 208, which implement a second level of the hierarchical decoding system. The read decoding circuit 206 is coupled to the main read bit lines (MBL_(r)), and the write decoding circuit 208 is coupled to the main write bit lines (MBL_(w)). The read decoding circuit 206 can be controlled to selectively couple the main read bit lines (MBL_(r)) to the read stage circuit 114, and the write decoding circuit 208 can be controlled to selectively couple the main write bit lines (MBL_(w)) to the write stage circuit 116.

In the read mode, a plurality of the switch 204 a are controlled by sets of first-level bias signals, denoted by YO<1:K>, where K is the number of local bit lines associated with a single main read bit line (MBL_(r)). The first-level bias signals YO<1:K> control the connections between the local bit lines (LBL) and the corresponding main read bit lines (MBL_(r)). Moreover, the connections between the main read bit lines (MBL_(r)) and the read stage circuit 114 are controlled by second-level bias signals, designated by YM. In embodiments, signals YO and YM regulate the bit line to a desired voltage value.

The read decoding circuit 206, the main read bit line (MBL_(r)), and the switch 204 b form a read path that connects the memory cell 104 to the read stage circuit 114 for a selected local bit line (LBL) and a memory cell 104 (i.e., the memory cell 104 electrically coupled to the selected local bit line (LBL) and the selected wordline (WL)).

The column decoder 112 includes, for each sector 202, at least a respective first-level decoding circuit for the read operations and write operations, which is coupled to the respective local bit lines (LBL) and can be activated for selecting the local bit lines (LBL).

The column decoder 112 further includes, for each set of sectors 202, a respective second-level decoding circuit for the read operations and write operations, which is coupled to the respective main bit lines (MBL) and can be activated for selecting the latter. Each first-level decoding circuit includes a respective first-level subcircuit for read operations and a respective first-level subcircuit for write operations. Each second-level decoding circuit includes a respective second-level subcircuit for read operations and a respective second-level subcircuit for the write operations. For example, the first-level subcircuits for read operations and the first-level subcircuits for write operations include, respectively, the switch 204 b and the switch 204 a. The second-level subcircuits for read operations and the second-level subcircuits for write operations form, respectively, the read decoding circuit 206 and the write decoding circuit 208.

In the K local bit lines (LBL) of a sector 202, the first-level subcircuit for the read operations coupled to sector 202 can be controlled electrically, by the first-level bias signals YO<1:K>, to electrically couple, each time, one of the K local bit lines (LBL)-in particular, the local bit line selected—to the corresponding main read bit line (MBL_(r)).

The second-level subcircuit for read operations can be controlled electrically by the second-level bias signals YM, to electrically couple the main read bit line (MBL_(r)) to the read stage circuit 114—coupling to the read stage circuit 114 enables bias of the selected main read bit line (MBL_(r)) and local bit line (LBL). Similar considerations apply to the first-level subcircuit for write operations coupled to sector 202, which couples the main write bit line (MBL_(w)) selected to the write stage circuit 116, also known as “program load.”

The non-volatile memory storage device 100 may be of the single-ended type, in which case the read stage circuit 114 is configured to compare the current that circulates in the memory cell 104 with a reference current to determine the stored data.

Alternatively, the non-volatile memory storage device 100 may be of the differential type, in which case data is programmed in pairs of memory cells 104 so that the cells of each pair store opposite data, and the read stage circuit 114 is configured to compare the currents that circulate in the memory cells 104 of the selected pair.

Regardless of whether the non-volatile memory storage device 100 is of a single-ended type or a differential type, the read stage circuit 114 includes a plurality of sense amplifiers. Each sense amplifier includes a first input and a second input. During the read operation, the first input of a sense amplifier is connected, in a way controlled by the column decoder 112, to a first selected memory cell 104 a, and the second input is connected to a second selected memory cell 104 b—in the case of differential reading-or to a reference-current generator-in the case of single-ended reading.

The sense amplifier generates an output that depends upon the comparison between the current that flows in the first selected memory cell 104 a and the current that flows in the second selected memory cell 104 b—in the case of differential reading-or in the reference-current generator-in the case of single-ended reading.

The sense amplifiers are connected to a supply voltage V_(dd), which may be rather low, for example, approximately equal to 1 Volt. Since the local bit lines (LBL) are biased at a voltage typically approximately equal to 0.6 Volts when selected, the sense amplifiers have an extremely small voltage margin available. A system and method that improves the operation of the sense amplifier given environmental conditions of the memory cell are, thus, desirable.

FIG. 3 illustrates an embodiment sense amplifier 300 for reading differential-type memory cells, as may be implemented in the non-volatile memory storage device 100.

Sense amplifier 300 includes a first bias transistor 302 a, a second bias transistor 302 b, a first pre-charge transistor 304 a, and a second pre-charge transistor 304 b. In embodiments, the first bias transistor 302 a, the second bias transistor 302 b, the first pre-charge transistor 304 a, and the second pre-charge transistor 304 b are of a P-channel enhancement-mode transistor type. In embodiments, the first bias transistor 302 a, the second bias transistor 302 b, the first pre-charge transistor 304 a, and the second pre-charge transistor 304 b are of the same type.

The source terminals of the first bias transistor 302 a, the second bias transistor 302 b, the first pre-charge transistor 304 a, and the second pre-charge transistor 304 b are electrically coupled to a supply voltage V_(dd). In embodiments, the voltage value of the supply voltage V_(dd) is equal to 1 V. The gate terminals of the first bias transistor 302 a and the second bias transistor 302 b are electrically coupled to a reference voltage V_(refp_sa). A signal sPRECH_N is present at the gate terminals of the first pre-charge transistor 304 a and the second pre-charge transistor 304 b. The drain terminals of the first bias transistor 302 a and the first pre-charge transistor 304 a are electrically coupled to each other, indicated by first input node SA<0>. Similarly, the drain terminals of the second bias transistor 302 b and the second pre-charge transistor 304 b are electrically coupled to each other, indicated by second input node SA<1>.

In embodiments, the first pre-charge transistor 304 a, and the second pre-charge transistor 304 b can be absent, in which case the precharging stage (described further below) is carried out on the basis of just the currents delivered by the first bias transistor 302 a and the second bias transistor 302 b.

The sense amplifier 300 further includes a first upper control transistor 306 a, second upper control transistor 306 b, a first lower control transistor 308 a, and a second lower control transistor 308 b. In embodiments, the first upper control transistor 306 a, the second upper control transistor 306 b, the first lower control transistor 308 a, and the second lower control transistor 308 b are of a P-channel enhancement-mode transistor type. In embodiments, the first upper control transistor 306 a, the second upper control transistor 306 b, the first lower control transistor 308 a, and the second lower control transistor 308 b are of the same type.

The source terminal of the first upper control transistor 306 a is electrically coupled to the drain terminals of the first bias transistor 302 a and the first pre-charge transistor 304 a. The first upper control transistor 306 a and the first lower control transistor 308 a are electrically coupled in series. In particular, the drain terminal of the first upper control transistor 306 a is electrically coupled to the source terminal of the first lower control transistor 308 a.

The source terminal of the second upper control transistor 306 b is electrically coupled to the drain terminals of the second bias transistor 302 b and the second pre-charge transistor 304 b. The second upper control transistor 306 b and the second lower control transistor 308 b are electrically coupled in series. In particular, the drain terminal of the second upper control transistor 306 b is electrically coupled to the source terminal of the second lower control transistor 308 b.

A signal sPRECH is present at the gate terminals of the first upper control transistor 306 a and the second upper control transistor 306 b. The singal sPRECH is equal to a logical negation of the signal sPRECH_N. In embodiments, the signals sPRECH and sPRECH_N are generated by the control logic 106. The value of the signals sPRECH and sPRECH_N vary between 0 V and the supply voltage Vdd (e.g., 1 V).

The gate terminals of the first lower control transistor 308 a and the second lower control transistor 308 b are electrically coupled to the reference voltage V_(refp_sa). However, in embodiments, the gate terminals of the first lower control transistor 308 a and the second lower control transistor 308 b can be set at a controlled voltage (i.e., a voltage generated starting from a voltage reference (for example, a bandgap circuit)), which is different from the reference voltage V_(refp_sa).

In embodiments, the first upper control transistor 306 a and the first lower control transistor 308 a can have positions reversed with respect to one another. Likewise, the second upper control transistor 306 b and the second lower control transistor 308 b can have positions reversed with respect to one another.

In embodiments, the first upper control transistor 306 a and the second upper control transistor 306 b may be absent. In such an embodiment, the gate terminal of the first lower control transistor 308 a and the second lower control transistor 308 b is set at the supply voltage V_(dd), in the periods of time during which the signal sPRECH is at ‘1,’ and is set at the reference voltage V_(refp_sa) (or at another controlled voltage) in the periods of time during which the signal sPRECH is at ‘0.’

The sense amplifier 300 further includes a first sense transistor 310 a, a second sense transistor 310 b, a first verify transistor 312 a, and a second verify transistor 312 b. In embodiments, the first sense transistor 310 a, the second sense transistor 310 b, the first verify transistor 312 a, and the second verify transistor 312 b are of an N-channel enhancement-mode transistor type. In embodiments, the first sense transistor 310 a, the second sense transistor 310 b, the first verify transistor 312 a, and the second verify transistor 312 b are of the same type. In such embodiments, the source terminals of the first sense transistor 310 a, the second sense transistor 310 b, the first verify transistor 312 a, and the second verify transistor 312 b is electrically coupled to ground.

The drain terminals of the first sense transistor 310 a and the first verify transistor 312 a are electrically coupled to the drain terminal of the first lower control transistor 308 a and the gate terminal of the second sense transistor 310 b, having a voltage referred to as the signal sCOMP_INT_N.

The drain terminals of the second sense transistor 310 b and the second verify transistor 312 b are electrically coupled to the drain terminal of the second lower control transistor 308 b and the gate terminal of the first sense transistor 310 a, having a voltage referred to as the signal sCOMP_INT. Signals sCOMP_INT_N and sCOMP_INT are logical negations of each other.

Thus, the first sense transistor 310 a and the second sense transistor 310 b are electrically coupled in a cross-coupled arrangement. Signal sEVAL_N is present on the gate terminals of the first verify transistor 312 a and the second verify transistor 312 b. In embodiments, the signal sEVAL_N is generated by the control logic 106. The value of the signal sEVAL_N varies between 0 V and the supply voltage Vdd.

The sense amplifier 300 further includes a first first-level transistor 318 a, a first second-level transistor 316 a, a second first-level transistor 318 b, and a second second-level transistor 316 b. In embodiments, the first first-level transistor 318 a, first second-level transistor 316 a, second first-level transistor 318 b, and second second-level transistor 316 b are of an N-channel enhancement-mode transistor type. In embodiments, the first first-level transistor 318 a, first second-level transistor 316 a, second first-level transistor 318 b, and second second-level transistor 316 b are of the same type.

The first first-level transistor 318 a and first second-level transistor 316 a are arranged in series. The drain terminal of the first second-level transistor 316 a is electrically coupled to the first input node SA<0>. The source terminal of the first second-level transistor 316 a is electrically coupled to the drain terminal of the first first-level transistor 318 a, which is electrically coupled with a first main bit line (MBL₁) of the non-volatile memory storage device 100. The source terminal of the first first-level transistor 318 a is electrically coupled to a first local bit line (LBL₁) of the non-volatile memory storage device 100 and a terminal of the storage element 108 a of a first memory cell 104 a.

The second first-level transistor 318 b and second second-level transistor 316 b are arranged in series. The drain terminal of the second second-level transistor 316 b is electrically coupled to the second input node SA<1>. The source terminal of the second second-level transistor 316 b is electrically coupled to the drain terminal of the second first-level transistor 318 b, which is electrically coupled with a second main bit line (MBL₂) of the non-volatile memory storage device 100. The source terminal of the second first-level transistor 318 b is electrically coupled to a second local bit line (LBL₂) of the non-volatile memory storage device 100 and a terminal of the access element 108 b of a second memory cell 104 b.

The first memory cell 104 a and the second memory cell 104 b are a pair of differential-type memory cells of the non-volatile memory storage device 100.

The signal YO, generated by column decoder 112, is present at the gate terminals of the first first-level transistor 318 a and the second first-level transistor 318 b. The signal YM, also generated by column decoder 112, is present at the gate terminals of the first second-level transistor 316 a and the second second-level transistor 316 b.

The first upper control transistor 306 a, the first lower control transistor 308 a, the first sense transistor 310 a, and the first verify transistor 312 a form a first branch of the sense amplifier 300.

The second upper control transistor 306 b, the second lower control transistor 308 b, the second sense transistor 310 b, and the second verify transistor 312 b form a second branch of the sense amplifier 300.

FIG. 4 illustrates an embodiment intermediate circuit 400 of the sense amplifier 300. The intermediate circuit 400 includes a first cross-coupled transistor 402 a, a second cross-coupled transistor 402 b, a first enable transistor 404 a, and a second enable transistor 404 b. In embodiments, the first cross-coupled transistor 402 a, second cross-coupled transistor 402 b, first enable transistor 404 a, and second enable transistor 404 b are P-channel enhancement-mode type transistors. In embodiments, the first cross-coupled transistor 402 a, second cross-coupled transistor 402 b, first enable transistor 404 a, and second enable transistor 404 b are the same as one another.

The source terminals of the first cross-coupled transistor 402 a, second cross-coupled transistor 402 b, first enable transistor 404 a, and second enable transistor 404 b are electrically coupled to the supply voltage V_(dd). The gate terminals of the first cross-coupled transistor 402 a and second cross-coupled transistor 402 b are connected, respectively, to the drain terminal of the second cross-coupled transistor 402 b and the drain terminal of the first cross-coupled transistor 402 a.

The source terminals of the first enable transistor 404 a and the second enable transistor 404 b are connected to the supply voltage V_(dd). The drain terminals of the first enable transistor 404 a and the second enable transistor 404 b are electrically coupled, respectively, to the drain terminals of the first cross-coupled transistor 402 a and the second cross-coupled transistor 402 b. A signal sEVAL, equal to the logical negation of the signal sEVAL_N is present on the gate terminals of the first enable transistor 404 a and the second enable transistor 404 b.

Moreover, the intermediate circuit 400 includes a first output transistor 406 a and a second output transistor 406 b. In embodiments, the first output transistor 406 a and second output transistor 406 b are N-channel enhancement-mode type transistors and are, for example, the same as one another.

The source terminals of the first output transistor 406 a and the second output transistor 406 b are electrically coupled to ground. The drain terminal of the first output transistor 406 a and the second output transistor 406 b are electrically coupled, respectively, to the first output node N_(out1) and the second output node N_(OUT2). The voltage present at each of the first output node N_(out1) and second output node _(Nout2) are referred to, respectively, as the signal sCOMP_OUT_N and the signal sCOMP_OUT.

The gate terminal of the first output transistor 406 a is electrically coupled to the drain of the second lower control transistor 308 b so as to receive the signal sCOMP_INT. The gate terminal of the second output transistor 406 b is electrically coupled to the drain of the first lower control transistor 308 a and receives the signal sCOMP_INT_N.

The pairs of logic values (sCOMP_INT, sCOMP_INT_N) and (sCOMP_OUT, sCOMP_OUT_N) are referred to, respectively, as the input state and the output state of the intermediate circuit 400.

FIG. 5 illustrates an embodiment timing diagram 500 for signals sCOMP_OUT_N, sCOMP_OUT, sPRECH, sPRECH_N, sEVAL, sEVAL_N, sCOMP_INT_N, and sCOMP_INT during a read operation.

In embodiments, the first first-level transistor 318 a, second second-level transistor 316 b, first second-level transistor 316 a, and second second-level transistor 316 b are in saturation where the bias signals YO and YM are set to a logical value equal to ‘1’. For example, the bias signals YO and YM are in the range between 1.2 and 1.4 V, which is higher than the supply voltage V_(dd) at 1 V. A voltage of about 0.6 V is present on the first bit line (LBL₁) and second bit line (LBL₂).

In embodiments, an enablement signal sWL_SEL is present on the gate terminals of the access elements 108 a of first memory cell 104 a and second memory cell 104 b (i.e., allows selection of the first memory cell 104 a and the second memory cell 104 b).

The reference voltage V_(refp_sa) is such that when first pre-charge transistor 304 a and second pre-charge transistor 304 b are inhibited, the first bias transistor 302 a and second bias transistor 302 b operate in saturation mode. Thus, a bias current I_(pol) passes through each of the first bias transistor 302 a and second bias transistor 302 b, which varies according to the particular type of reading procedure.

The reference voltage V_(refp_sa), first bias transistor 302 a, and second bias transistor 302 b form current mirrors that can be controlled by, for example, the control logic 106. As detailed herein, the embodiment regulator 700 of FIG. 7 is configured to adjust the value of the bias current I_(pol) to mitigate environmental (e.g., temperature) variations tied to the memory cell behavior.

As shown in FIG. 5 , the sense amplifier 300 includes a precharging stage from time t₀ to time t₁. At time t₀, signal sEVAL is equal to ‘0’ corresponding to a null voltage, whereas the signal sPRECH has the value ‘1’ corresponding to the supply voltage V_(dd). At the instant time t₀, the signal sPRECH_N is ‘0’. Thus, the first pre-charge transistor 304 a and second pre-charge transistor 304 b operate in the linear region. The current passing through the first pre-charge transistor 304 a and second pre-charge transistor 304 b is equal to a pre-charge current I_(PRECH), typically around 100 µA.

Further, the first bias transistor 302 a and the second bias transistor 302 b operate in the linear region. Thus, the bias current I_(pol), which is less than the pre-charge current I_(PRECH), passes through each of the first bias transistor 302 a and second bias transistor 302 b.

A current I_(i1) equal to the sum of the bias current I_(pol) and pre-charge current I_(PRECH), from the first bias transistor 302 a and the first pre-charge transistor 304 a flows to the first input node SA<o>.

Likewise, a current I_(i2) equal to the sum of the bias current I_(pol) and pre-charge current I_(PRECH), from the second bias transistor 302 b and the second pre-charge transistor 304 b, flows to the second input node SA<1>.

Further, at time t_(o), the first upper control transistor 306 a, second upper control transistor 306 b, first lower control transistor 308 a, and second lower control transistor 308 b are inhibited.

Thus, from time t₀ to time t₁, a current that flows into the first MBL equal to the sum of the bias current I_(pol) and pre-charge current I_(PRECH). As a result, the capacitance 320 a formed by the first main bit line (MBL₁) is charged during a transient of negligible duration.

Likewise, from time t₀ to time t₁, a current that flows into the second memory cell 104 b, designated with I_(cell2), equal to the sum of the bias current I_(pol) and pre-charge current I_(PRECH). And, the capacitance 320 b formed by the second main bit line (MBL₂) is charged during the transient of negligible duration.

The currents I_(cell1) and I_(cell2) that flow, respectively, in the first memory cell 104 a and the second memory cells 104 b depend upon the values of resistance of the storage elements 108 a, and therefore upon the data stored.

In addition, at the instant t₀, the signal sEVAL_N is equal to ‘1’ and signal sEVAL is equal to ‘0.’ Thus, the first verify transistor 312 a and the second verify transistor 312 b operate in the linear region. Consequently, the shared node between drain terminals of the first sense transistor 310 a, first verify transistor 312 a, first lower control transistor 308 a, and the gate terminal of the second sense transistor 310 b is forced to ground. Likewise, the shared node between drain terminals of the second sense transistor 310 b, second verify transistor 312 b, second lower control transistor 308 b, and the gate terminal of the first sense transistor 310 a is forced to ground. Thus, the signals sCOMP_INT and s_COMP_INT_N are equal to ‘0.’ As a result, the first sense transistor 310 a and second sense transistor 310 b are OFF between time t₀ and time t₁.

Because the signals sCOMP_INT and sCOMP_INT_N are equal to ‘0,’ the first output transistor 406 a and second output transistor 406 b of the intermediate circuit 400 are inhibited between time t₀ and time t₁. Further, as the signal sEVAL is equal to ‘0,’ the first enable transistor 404 a and the second enable transistor 404 b are above the threshold, which forces the logic values of signals sCOMP_OUT and sCOMP_OUT_N to be ‘1.’ Thus, the first cross-coupled transistor 402 a and the second cross-coupled transistor 402 b are below the threshold.

The sense amplifier 300 includes an unbalancing stage from time t₁ to time At time t₁, at the end of the pre-charging stage, the logic value of signals sPRECH and sPRECH_N switch to, respectively, ‘0’ and ‘1.’ Thus, at time t₁, the first pre-charge transistor 304 a and the second pre-charge transistor 304 b switch OFF. As a result, the pre-charge current I_(prech) is no longer flowing through the first pre-charge transistor 304 a and second pre-charge transistor 304 b.

During time t₁ to time t₂, the signal sEVAL_N remains equal to ‘1’ and signal sEVAL remains equal to ‘0.’ Thus, the shared node between drain terminals of the first sense transistor 310 a, first verify transistor 312 a, first lower control transistor 308 a, and the gate terminal of the second sense transistor 310 b remains at ground. Likewise, the shared node between drain terminals of the second sense transistor 310 b, second verify transistor 312 b, second lower control transistor 308 b, and the gate terminal of the first sense transistor 310 a remains at ground. The signals sCOMP_INT and s_COMP_INT_N remain equal to ‘0’ and signals sCOMP_OUT and sCOMP_OUT_N remain equal to ‘1.’

Because the signal sPRECH turns to ‘0’ at instant time t₁, the first upper control transistor 306 a and the second upper control transistor 306 b switch ON and being operating in linear mode. Further, the first lower control transistor 308 a and the second lower control transistor 308 b switch ON and being operating in saturation mode.

At time t₁, a current designated as I_(branch1) flows in the first upper control transistor 306 a. The value of the current I_(branch1) is equal to the bias current I_(pol) minus the current I_(cell1) flowing in the first memory cell 104 a. Likewise, a current designated as I_(branch2) flows in the second upper control transistor 306 b. The value of the current I_(branch2) is equal to the bias current I_(pol) minus the current I_(cell2) flowing in the second memory cell 104 b.

In an exemplary embodiment, where the first memory cell 104 a is in SET state and the second memory cell 104 b is in RESET state, I_(cell1) is greater than I_(cell2). In this exemplary embodiment, I_(branch1) is less than I_(branch2)—FIG. 5 is a representative timing diagram of such an exemplary embodiment.

During the unbalancing stage, the current I_(branch1) is flowing through the first upper control transistor 306 a and first lower control transistor 308 a, which is different from the current I_(branch2) flowing through the second upper control transistor 306 b and second lower control transistor 308 b. Thus, the branches of sense amplifier 300 are unbalanced. Since from time t₁ to time t₂ the signal sEVAL_N and sEVAL are kept at, respectively, ‘1’ and ‘0’; the signals sCOMP_INT and s_COMP_INT_N are still forced to ground.

Finally, the sense amplifier 300 includes the verify stage from time t₂ to time t₃. Time t₃ indicates an ending of the verify stage.

At instant time t₂, and at the start of the verify stage, the signal sEVAL_N and sEVAL switch to, respectively, ‘0’ and ‘1.’ Thus, at time t₂, the first verify transistor 312 a and the second verify transistor 312 b switch OFF-no longer forcing signals sCOMP_INT_N and sCOMP_INT to ground.

As currents I_(branch1) and I_(branch2) flow through, respectively, the first lower control transistor 308 a and second lower control transistor 308 b, the voltage at the drain node of each of the first lower control transistor 308 a and second lower control transistor 308 b increase from time t₂ to time t₃. In the exemplary embodiment of FIG. 5 , where the first memory cell 104 a is in SET state and the second memory cell 104 b is in RESET state and I_(branch2) is greater than I_(branch1), the voltage at the drain node of the second lower control transistor 308 b increases more rapidly than the voltage at the drain node of the first lower control transistor 308 a.

As detailed previously, the drain node of the second lower control transistor 308 b is electrically coupled to the gate of the first sense transistor 310 a, and the drain node of the first lower control transistor 308 a is electrically coupled to the gate of the second sense transistor 310 b. Thus, the gate of a transistor having the faster rise time forces the other transistor to being OFF. In the exemplary embodiment where the first memory cell 104 a is in SET state and the second memory cell 104 b is in RESET state, the first sense transistor 310 a is turned ON and the second sense transistor 310 b is turned OFF in the sense state. As a result, slightly after time t₂, the signal sCOMP_INT switches to ‘1,’ while sCOMP_INT_N remains at ‘0.’

Alternatively, in an exemplary embodiment where the first memory cell 104 a is in RESET state and the second memory cell 104 b is in SET state, slightly after time t₂, the signal sCOMP_INT remains at ‘0,’ while sCOMP_INT_N switches to ‘1.’

Thus, signals sCOMP_INT and sCOMP_INT_N, as complementary logic values, provide a corresponding high or low value as a function of the datum stored in the differential memory cell pairing of the first memory cell 104 a and second memory cell 104 b.

The first upper control transistor 306 a, first lower control transistor 308 a, second upper control transistor 306 b, and second lower control transistor allow current I_(branch1) and I_(branch2) to remain substantially constant during the verify stage, improving the sensitivity of the sense amplifier 300.

The signals sCOMP_INT_N and sCOMP_INT are passed as inputs to the intermediate circuit 400. Thus, in the sense state where one of the signals sCOMP_INT_N and sCOMP_INT is high and the other is low, the output of the intermediate circuit 400 (i.e., sCOMP_OUT_N and sCOMP_OUT) changes from equal logic values (e.g., ‘1’ ‘1’) to complementary logic values (e.g., ‘1’ ‘0’).

In the exemplary embodiment where the first memory cell 104 a is in SET state and the second memory cell 104 b is in RESET state, signal sCOMP_INT switches to ‘1,’ while sCOMP_INT_N remains at ‘0.’ Thus, the first output transistor 406 a switches ON, which forces the first output node N_(OUT1) to ground. As a result, the signal sCOMP_OUT_N is changed from ‘1’ to ‘0.’ The second output transistor 406 b remains inhibited, and the signal sCOMP_OUT remains at ‘1.’

Further, as the signal sEVAL switches from logic ‘0’ to logic ‘1’ at time t₂, the first enable transistor 404 a and the second enable transistor 404 b drop below the threshold. The first cross-coupled transistor 402 a remains inhibited because the gate terminal of the first cross-coupled transistor 402 a remains at ‘1.’ The second cross-coupled transistor 402 b switches ON and operates in saturation mode because the gate terminal of the second cross-coupled transistor 402 b switches to ‘0.’

Thus, at the instant time t₂, the signals sCOMP_INT and sCOMP_INT_N change from the precharging state of '0' and ‘0’ to the sensed state (e.g., '1' and ‘0,’ respectively), which changes the output signals sCOMP_OUT and sCOMP_OUT_N from the '1' and '1' stage to, for example, '1' and '0' state.

Signals sCOMP_OUT and sCOMP_OUT_N have dynamics that substantially extend over the entire range [0-V_(dd)], unlike the signals sCOMP_INT and sCOMP_INT_N, the dynamics of which are more limited, on account of the voltage drop that occurs between the source and drain terminals of the first bias transistor 302 a and the second bias transistor 302 b.

FIG. 6 illustrates an embodiment latch circuit 600 of the sense amplifier 300. The latch circuit 600 includes a first NAND gate 604 and a second NAND gate 606. The signal sCOMP_OUT_N is coupled to the input of the first NAND gate 604, and the signal sCOMP_OUT is coupled to the input of the second NAND gate 606. As discussed previously, the signals sCOMP_OUT_N and sCOMP_OUT are electrically coupled to, respectively, the first output node N_(out1) and second output node N_(OUT2) of the intermediate circuit 400. Optionally (not shown), latch circuit 600 may include an input sRESET, which is coupled to an output of the control logic 106 to receive the sRESET signal. Latch circuit 600 includes a pair of outputs, at the output of the first NAND gate 604 and the second NAND gate 606, which generate complementary signals sQN and sQ.

The output signals sQ and sQN are equal to ‘1’ and ‘0,’ respectively, when the signals sCOMP_OUT and sCOMP_OUT_N are equal to ‘1’ and ‘0’ during the verify stage. The output signals sQ and sQN keep their state during the pre-charging stage.

Embodiments of this disclosure accommodate the operation of a sense amplifier having a large temperature range, for example, from about - 40° C.elcius (°C) to about + 175° C. In embodiments, this disclosure provides for an increased variation range of the polarization current (I_(pol)) of the sense amplifier.

Although, this disclosure provides exemplary regulators that can be used with respect to a sense amplifier as disclosed herein, it should be readily appreciated that these exemplary regulators may be used in combination with other sense amplifiers to similarly provide for an increased variation range of current, such as a polarization current that is variable with temperature.

FIG. 7 illustrates an embodiment regulator 700, as may be implemented in the sense amplifier 300. Regulator 700 includes a common operational amplifier (op-amp) 702 arranged in a voltage follower circuit configuration to provide a voltage controlled current source.

The first input (i.e., inverting input) of the op-amp 702 is connected to a reference voltage (V_(REF)). The second input (i.e., non-inverting input) of the op-amp 702 is connected to the drain terminal of transistor 704 having a voltage V_(feedback). In reference to FIG. 3 , the transistor 704 represents the first bias transistor 302 a or second bias transistor 302 b.

The output of the op-amp 702 is connected to the gate terminal of transistor 704, which has a regulated voltage V_(repf_sa). In embodiments, with respect to FIG. 3 , the output of the op-amp 702 is connected to the gate terminals of the first bias transistor 302 a, second bias transistor 302 b, first lower control transistor 308 a, and second lower control transistor 308 b. The source terminal of transistor 704 is coupled to the supply voltage V_(dd).

The regulator 700 is configured to adjust the value of the bias current I_(pol) generated by the first bias transistor 302 a and the second bias transistor 302 b to mitigate and account for environmental (e.g., temperature) variations in the memory cells.

As previously noted, sensing which of the first memory cell 104 a or second memory cell 104 b is in the SET or RESET state depends on the values of the currents I_(branch1) and I_(branch2). During the verify stage the sense amplifier is configured in single ended mode, and it evaluates the difference between a respective cell current I_(cell) and a reference current-here, current I_(ref).

In particular memory types, such as in phase-change memory (PCM), the temperature has an impact on the current value of the cell current I_(cell) in the few microseconds after the write pulse(i.e., during the verify operation).

Because the difference in current between the two branches of sense amplifier 300 is in the microamp range, to maintain an accurate reading of the memory cells, it is desirable to discriminate this difference in a controlled current window in all temperature ranges.

In embodiments, regulator 700—in the sense amplifier 300 used to read differential-type memory cells—is regulated with respect to the maximum value of the current I_(cell) of the least conductive memory cell of the pair of differential memory cells. The least conductive memory cell between the first memory cell 104 a and the second memory cell 104 b is the memory cell that is in RESET state. Thus, regulator 700 regulates the voltage V_(repf_sa) such that I_(pol) is equal to the sum of I_(cell_RESET_max) and 10 µA (I_(pol)=I_(cell_RESET_max) + 10 µA), where I_(cell_RESET_max) is the maximum value of current I_(cell) in the memory cell being in the RESET state. It should be appreciated that the fixed current value of 10 µA is non-limiting, and in embodiments, the value of the fixed current value may be less than or greater than 10 µA. In some embodiments, the value of the fixed current value is between (and including) 5 and 80 microamps.

Thus, the value of the voltage V_(REF) at the inverting input of op-amp 702 is set to provide a voltage V_(repf_sa), which in turn provides a current I_(pol) equal to I_(cell_RESET_max) + 10 µA.

Advantageously, the regulator 700 provides a speedy solution without compromising the sensing accuracy by the sense amplifier 300.

In embodiments, the finite state machine circuit 120, the control logic 106, or a controller 1102 of the device 1100 incorporating the non-volatile memory storage device 100 varies the value of the reference voltage (V_(REF)) of the op-amp 702 based on a list provided in memory. The list or table provides a reference voltage (V_(REF)) for each kind of operation and for each temperature range. This second information can be provided by an external temperature sensor. In such an embodiment, the list or table of corresponding reference voltage (V_(REF)) values are stored in on-board memory 122, a memory of a device incorporating the non-volatile memory storage device 100, for example, the random-access memory 1108 described with respect to FIG. 12 , or inside a dedicated sector of the PCM itself.

FIG. 8 illustrates an embodiment sense amplifier 800 for reading single-ended type memory cells, as may be implemented in the non-volatile memory storage device 100. In the sense amplifier 800, the first branch is electrically coupled to the first memory cell 104 a. In contrast to the sense amplifier 300, sense amplifier 800 does not have a second memory cell 104 b in the second branch. In embodiments, the voltage V_(dd) is approximately 1 V, and the voltage at the bit line is about 0.6 V.

In sense amplifier 800, the source terminal of the second first-level transistor 318 b is electrically coupled to a current sink circuit 802, instead of the second memory cell 104 b in sense amplifier 300. The current sink circuit 802 generates a reference current I_(DAC) by a digital-to-analog converter (DAC). The reference current I_(DAC) plays a similar role to that of the current I_(cell2) in the second branch of sense amplifier 300.

Comparable to sense amplifier 300, in sense amplifier 800, sensing whether first memory cell 104 a is in the SET or RESET state depends on the values of the currents I_(branch1) and I_(branch2). During the verify stage, the current I_(branch1) is equal to the difference between I_(pol) and I_(cell1), and the current I_(branch2) is equal to the difference between I_(pol) and I_(DAC). Thus, during the verify stage, the sense amplifier 800 evaluates a difference between the cell current I_(cell1) and current I_(pol) in the first branch with the difference between I_(DAC) and I_(pol) in the second branch.

FIG. 9 illustrates an embodiment regulator 900, as may be implemented in the sense amplifier 800. Regulator 900 includes a common operational amplifier (op-amp) 902 and the current sink 906.

The first input (i.e., inverting input) of the op-amp 902 is connected to a reference voltage (V_(REF)). The second input (i.e., non-inverting input) of the op-amp 902 is electrically coupled to the drain terminal of transistor 904 having a voltage V_(feedback). The second input of the op-am 902 is, additionally, electrically coupled to the current sink 906. Additional information related to the current sink 906 is provided in reference to FIG. 11 . In reference to FIG. 8 , transistor 904 represents the first bias transistor 302 a or second bias transistor 302 b. The output of the op-amp 902 is connected to the gate terminal of transistor 904, which has a regulated voltage V_(repf)__(sa). In embodiments, with respect to FIG. 8 , the output of the op-amp 902 is connected to the gate terminals of the first bias transistor 302 a, second bias transistor 302 b, first lower control transistor 308 a, and second lower control transistor 308 b. The source terminal of transistor 904 is coupled to the supply voltage V_(dd).

The regulator 900 is configured to adjust the value of the bias current I_(pol) based on the reference current I_(ref) in the reference branch of the sense amplifier 800. Thus, regulator 900 regulates the voltage V_(repf_sa) based on the current value of the reference current I_(ref) used in the reference branch (i.e., second branch) of sense amplifier 800. Specifically, the regulator 900 regulates the voltage V_(repf_sa) such that I_(pol) is equal to I_(ref) + 10 µA (I_(pol)=I_(ref) + 10 µA). As a result, during the verify stage, the sense amplifier 800 becomes independent of the reference current I_(ref) by maintaining I_(branch2)=I_(Pol)-I_(ref)=10 µA. The temperature dependent contribution current (I_(temp)) is taken into account inside I_(ref) generation (i.e., I_(ref)=I_(DAC) + I_(temp)) and it is configured according to the external temperature sensor code and the look up table in the digital controller. Thus, the reference current I_(ref) and the current I_(pol) are aligned to the behaviour of the memory cell across temperatures, and the accuracy of the sensing becomes independent of the reference current I_(DAC). It should be appreciated that the fixed current value of 10 µA is non-limiting, and in embodiments, the value of the fixed current value may be less than or greater than 10 µA. In some embodiments, the value of the fixed current value is between (and including) 5 and 80 microamps. In embodiments, the value of the temperature dependent contribution current (I_(temp)) is between (and including) 1 to 25 microamps.

FIG. 10 illustrates an embodiment current sink circuit 802, as maybe implemented in the sense amplifier 800. The current sink circuit 802 includes a first multiplexer 1002 and a second multiplexer 1004.

The first multiplexer 1002 includes inputs 1006 a-c and output 1008. The output 1008 is coupled to a first configurable current sink 1010 to generate the current I_(DAC). The inputs 1006 a-b correspond to one of SET or RESET verify conditions of the reference current I_(DAC) used in the second branch of the sense amplifier 800. The input 1006 c corresponds to a selection between one of the SET or RESET conditions, which may be performed by the finite state machine circuit 120, the control logic 106, or a controller 1102 of the device 1100 incorporating the non-volatile memory storage device 100. During the memory program a sequence of SET program pulses and RESET program pulses is performed through the finite state machine 120. Moreover each program pulse is followed by a verify operation configured according to the kind of pulse that was applied. Once the first multiplexer 1002 receives a signal at the input 1006 c, a control signal corresponding to one of the SET or RESET conditions are provided to an input of the first configurable current sink 1010 to generate the current I_(DAC).

The second multiplexer 1004 includes inputs 1012 a-n, input 1016, and output 1014. The output 1014 is coupled to a second configurable current sink 1018 to generate the temperature dependent contribution current I_(TEMP). The inputs 1012 a-n correspond to N number of temperature configurations stored, for example, in on-board memory 122 or a memory of a device incorporating the non-volatile memory storage device 100, for example, the random-access memory 1108 described with respect to FIG. 12 . The second multiplexer 1004 receives a temperature setting signal at input 1016 based on a sensed temperature of the memory cell or non-volatile memory storage device 100. In embodiments, the finite state machine circuit 120 provides the temperature setting signal at input 1016. In some embodiments, the control logic 106 provides the temperature setting signal at input 1016. In other embodiments, a controller 1102 of the device 1100 incorporating the non-volatile memory storage device 100 provides the temperature setting signal at input 1016—see FIG. 12 .

The multiplexer selects between the various control signals at inputs 1012 a-n to appropriately set the second configurable current sink 1018 based on the temperature setting signal received at input 1016. As a result, the second configurable current sink 1018 generates a corresponding current value for I_(TEMP) based on the sensed temperature. In embodiments, the value of the temperature dependent contribution current (I_(temp)) is between (and including) 1 to 25 microamps.

FIG. 11 illustrates an embodiment current sink circuit 906, as may be implemented in the regulator 900. The current sink 906 is similar to the current sink 802. In addition, however, current sink 906 includes a fixed current sink 1120 to generate the fixed current I_(FIXED). In embodiments, the current value of the fixed current I_(FIXED) is equal to 10 µA. However, this value is non-limiting and currents greater than or less than 10 µA are also contemplated. In some embodiments, the value of the fixed current value is between (and including) 5 and 80 microamps.

The current sunk through first configurable current sink 1010, second configurable current sink 1018, and fixed current sink 1120 acts as a current sunk through, for example, a shunt resistor in a voltage controlled current source configuration. Thus, by adjusting the current values I_(DAC), I_(TEMP), and I_(FIXED), the current sink circuit 906 produces a drop in voltage and the non-inverting input of the op-amp 902 correspondingly adjusts the voltage V_(repf_sa), given V_(REF).

The current sink circuit 906 in the regulator 900 and the current sink 802 in the sense amplifier 800 act in unison such that the correspondingly generated I_(DAC) and I_(TEMP) values are equal in value.

FIG. 12 illustrates an electronic device 1200 incorporating the non-volatile memory storage device 100. The electronic device 1200 may be, for example, a personal digital assistant (PDA), a portable or desktop computer, possibly with the capacity of wireless data transfer, a mobile phone, a digital audio player, a camera or a camcorder, or the like, capable of processing, storing, transmitting, and receiving information.

The electronic device 1200 includes the controller 1202 (e.g., a microcontroller, microprocessor, processor, or the like), an interface 1204 (e.g., keyboard, display, or the like) to input and display data, the non-volatile memory storage device 100, a wireless interface 1206 (e.g., antenna, or the like) for transmitting and receiving data through a radiofrequency wireless communication network, random-access memory (RAM) 1208, a battery 1210 used to supply power to the electronic device 1200, and optional camera 1212. The various components of the electronic device 1200 are coupled through a bus 1214. The controller 1202 can control the non-volatile memory storage device 100 by, for example, co-operating with the control logic 106.

Although the description has been described in detail, it should be understood that various changes, substitutions, and alterations may be made without departing from the spirit and scope of this disclosure as defined by the appended claims. The same elements are designated with the same reference numbers in the various figures. Moreover, the scope of the disclosure is not intended to be limited to the particular embodiments described herein, as one of ordinary skill in the art will readily appreciate from this disclosure that processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, may perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

It is understood that the embodiments of this disclosure are not limited to applications disclosed herein regarding the measurement of a voltage drop at a reserve capacitor in a supplemental restraint system. The various embodiments are also applicable to other applications that benefit from measuring a voltage drop at a terminal of an electronic circuit having an unknown baseline voltage.

The specification and drawings are, accordingly, to be regarded simply as an illustration of the disclosure as defined by the appended claims, and are contemplated to cover any and all modifications, variations, combinations, or equivalents that fall within the scope of the present disclosure. 

What is claimed is:
 1. A non-volatile memory storage device, comprising: an array of memory cells of a differential type, the array of memory cells comprising a plurality of pair of memory cells, each pair of memory cells having a first memory cell and a second memory cell, the first memory cell being in one of a SET state or a RESET state and the second memory cell being in a state other than that of the first memory cell; a sense amplifier comprising a first branch coupled to a first memory cell and a second branch coupled to a second memory cell, the sense amplifier configured to: generate a first bias current in the first branch by a first transistor of the sense amplifier, generate a second bias current in the second branch by a second transistor of the sense amplifier, the first bias current being the same as the second bias current, sense a first delta current corresponding to a difference between the first bias current and a current flowing in the first memory cell, and sense a second delta current corresponding to a difference between the second bias current and a current flowing in the second memory cell; and a regulator coupled to the sense amplifier, the regulator configured to generate a regulated voltage to gate terminals of the first transistor and the second transistor of the sense amplifier, the regulated voltage generated such that the first bias current and the second bias current have a current value equal to the sum of a maximum current flowing in a memory cell being in a RESET state and a fixed current.
 2. The non-volatile memory storage device of claim 1, wherein a value of the fixed current is between 5 and 80 microamps.
 3. The non-volatile memory storage device of claim 1, wherein source terminals of the first transistor and the second transistor are coupled to a supply voltage having a voltage of approximately 1 Volts.
 4. The non-volatile memory storage device of claim 1, wherein the regulator comprises an operational amplifier (op-amp) having a non-inverting input coupled to a drain terminal of the first transistor and an inverting input coupled to a reference voltage.
 5. The non-volatile memory storage device of claim 1, wherein the first memory cell is in a SET state and the second memory cell is in the RESET state, and the current flowing in the first memory cell being greater than the current flowing in the second memory cell.
 6. The non-volatile memory storage device of claim 1, wherein the first memory cell is in a SET state and the second memory cell is in the RESET state, and the second memory cell being a lesser conductive memory cell than the first memory cell.
 7. The non-volatile memory storage device of claim 1, further comprising a memory used to store a list of reference voltage values corresponding to each particular pair of memory cells of the array of memory cells, and the regulated voltage is generated such that the current value being equal to the sum of the maximum current flowing in the memory cell being in the RESET state is particular to each memory cell pairing of the array of memory cells.
 8. A non-volatile memory storage device, comprising: an array of memory cells of a single-ended type, each memory cell being in one of a SET state or a RESET state; a sense amplifier comprising a first branch coupled to a memory cell and a second branch coupled to a reference current source, the sense amplifier configured to: generate a first bias current in the first branch by a first transistor of the sense amplifier, generate a second bias current in the second branch by a second transistor of the sense amplifier, the first bias current being the same as the second bias current, sense a first delta current corresponding to a difference between the first bias current and a current flowing in the memory cell, and sense a second delta current corresponding to a difference between the second bias current and a reference current generated by the reference current source; and a regulator coupled to the sense amplifier, the regulator configured to generate a regulated voltage to gate terminals of the first transistor and the second transistor of the sense amplifier, the regulated voltage generated such that the first bias current and the second bias current have a current value equal to the sum of a fixed current and the reference current generated by the reference current source across temperature.
 9. The non-volatile memory storage device of claim 8, wherein a value of the fixed current is between 5 and 80 microamps.
 10. The non-volatile memory storage device of claim 8, wherein source terminals of the first transistor and the second transistor are coupled to a supply voltage having a voltage of approximately 1 Volts.
 11. The non-volatile memory storage device of claim 8, wherein the regulator comprises an operational amplifier (op-amp) having a non-inverting input and an inverting input, the non-inverting input coupled to a drain terminal of the first transistor and the reference current source, and the inverting input coupled to a reference voltage.
 12. The non-volatile memory storage device of claim 8, wherein the reference current source comprises a digital-to-analog circuit, the reference current source being generated by the digital-to-analog circuit, and the reference current is adjusted based on a temperature reading of the non-volatile memory storage device.
 13. The non-volatile memory storage device of claim 8, wherein the regulator comprises an operational amplifier (op-amp) having a non-inverting input coupled to a drain terminal of the first transistor, the non-inverting input further coupled in a shunt configuration with the reference current source.
 14. The non-volatile memory storage device of claim 13, wherein the reference current source comprises a multiplexer and a configurable current sink, the multiplexer configured to adjust the configurable current sink based on a sensed temperature of the non-volatile memory storage device.
 15. A device, comprising: an array of memory cells of a single-ended type, each memory cell being in one of a SET state or a RESET state; a sense amplifier comprising a first branch coupled to a memory cell and a second branch coupled to a reference current source, the sense amplifier configured to: generate a first bias current in the first branch by a first transistor of the sense amplifier, generate a second bias current in the second branch by a second transistor of the sense amplifier, the first bias current being the same as the second bias current, sense first delta current corresponding to a difference between the first bias current and a current flowing in the memory cell, and sense a second delta current corresponding to a difference between the second bias current and a reference current generated by the reference current source; a regulator coupled to the sense amplifier, the regulator configured to generate a regulated voltage to gate terminals of the first transistor and the second transistor of the sense amplifier, the regulated voltage generated such that the first bias current and the second bias current have a current value equal to the sum of a fixed current and the reference current generated by the reference current across temperature; and a controller coupled to the regulator, sense amplifier, and the array of memory cells, the controller configured to generate a control signal to the regulator to generate the regulated voltage.
 16. The device of claim 15, wherein a value of the fixed current is between 5 and 80 microamps.
 17. The device of claim 15, wherein source terminals of the first transistor and the second transistor are coupled to a supply voltage having a voltage of approximately 1 Volts.
 18. The device of claim 15, wherein the regulator comprises an operational amplifier (op-amp) having a non-inverting input coupled to a drain terminal of the first transistor, the non-inverting input further coupled in a shunt configuration with the reference current source.
 19. The device of claim 18, wherein the reference current source comprises a multiplexer and a configurable current sink, the multiplexer configured to adjust the configurable current sink based on a sensed temperature of the array of memory cells.
 20. The device of claim 15, wherein the reference current generated by the reference current source is adjusted based on a temperature reading of the array of memory cells, and wherein the reference current is adjusted based on temperature between 1 and 25 microamps. 